Image sensors are semiconductor devices that convert optical images into electrical signals. Image sensors are mainly classified as a CCD (charge coupled device) image sensor or a CMOS (complementary metal oxide silicon) image sensor.
The CMOS image sensor includes a photodiode and a MOS transistor in each unit pixel, and sequentially detects the electric signals of each unit pixel in a switching mode to realize images.
The CMOS image sensor includes a photodiode region for converting light signals into electric signals and a transistor for processing the electric signals. Typically, the photodiode region and the transistor are horizontally aligned on a semiconductor substrate.
According to the horizontal CMOS image sensor, a photodiode and the transistor are horizontally aligned on the substrate such that they are adjacent to each other. Thus, an additional area of the substrate is required for each unit pixel to form the photodiode.